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The microbiocidal activity of glutaraldehyde was inactivated by reaction with sodium bisulfite via formation of a proposed glutaraldehyde-bisulfite complex. High-performance liquid chromatography (HPLC) analysis of 2% (0.2M) alkaline glutaraldehyde indicated complete loss of glutaraldehyde at a 2.2:1 molar ratio of sodium bisulfite to glutaraldehyde. Neither 1.7% (0.17 M) sodium bisulfite alone nor the glutaraldehyde-bisulfite complex was microbiocidal when tested against Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, and Polybac Polyseed BOD seed inoculum. Bacterial inhibition tests indicated that the glutaraldehyde-sodium bisulfite complex had no effect on the growth of sewage microorganisms at concentrations as high as 50-100 ppm (5 x 10(-4)-1 x 10(-3) M), with an IC50 of 230-440 ppm (2.3 x 10(-3)-4.4 x 10(-3) M), based on glutaraldehyde concentration. A 28-close bottle test showed a 5-d biodegradation of 48% and 51%, and a 15-d biodegradation of 57% and 63% for 3:1 and 2.2:1 bisulfite to glutaraldehyde molar ratios, respectively. Acute aquatic toxicity testing with Daphnia magna demonstrated an LC50 of 41-109 ppm (4.1 x 10(-4)-10.9 x 10(-4) M) and a no-observed-effect concentration (NOEC) of 16 ppm (1.6 x 10(-4) M) for the proposed glutaraldehyde-bisulfite complex (based on glutaraldehyde concentration), approximately 10-fold higher than found for glutaraldehyde alone, indicating that the proposed glutaraldehyde-bisulfite complex is less toxic to the environment than glutaraldehyde.